feat(php-shim): give ported exceptions PHP's class hierarchy

Ported exceptions were flat structs reached with `downcast_ref`, so
Composer's `catch (\RuntimeException $e)` only matched the exact leaf
type and `get_class($e)` had nothing to report. Each exception now
embeds an instance of the class it extends and travels inside an
`AnyThrowable`; `Catch::catch`/`catch_mut` walk that chain, and
`PhpClass::php_class_name` yields the PHP FQCN.

Dropping the `std::error::Error` impls from the exception types leaves
`AnyThrowable` as the only route into an `anyhow::Error`, so the walk
cannot be bypassed. A `no_exception_downcast` linter catches the
`downcast::<X>()` calls that would now silently answer `None`.

Three sites change behavior as a result: the `TransportException`
exit-code override reaches `MaxFileSizeExceededException`, the
`catch (\LogicException)` in findSimilar() reaches its subclasses, and
rendered exception titles carry the real class name rather than a
guess. `get_class_err()` is no longer a `todo!()`, which re-enables
FilesystemRepositoryTest::testCorruptedRepositoryFile.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 8 insertions, 10 deletions

diff --git a/crates/shirabe/src/downloader/filesystem_exception.rs b/crates/shirabe/src/downloader/filesystem_exception.rs
index f0aa831f..6e90e328 100644
--- a/crates/shirabe/src/downloader/filesystem_exception.rs
+++ b/crates/shirabe/src/downloader/filesystem_exception.rs
@@ -7,17 +7,15 @@ pub struct FilesystemException(pub Exception);
 
 impl FilesystemException {
     pub fn new(message: String, code: i64) -> Self {
-        FilesystemException(Exception {
-            message: format!("Filesystem exception: \n{}", message),
+        FilesystemException(Exception::with_code(
+            format!("Filesystem exception: \n{}", message),
             code,
-        })
+        ))
     }
 }
 
-impl std::fmt::Display for FilesystemException {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.0.fmt(f)
-    }
-}
-
-impl std::error::Error for FilesystemException {}
+shirabe_php_shim::impl_php_exception!(
+    FilesystemException,
+    0,
+    r"Composer\Downloader\FilesystemException"
+);